How to reduce weld shrinkage that is warping my parts?

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I need recommendations on what procedural steps are useful for reducing weld shrinkage that is warping my work. I am welding two streamlined tubes (1 1/2 inch equivalent diameter),  0.049 inch wall, 4130 steel tubes that are arranged in a shallow V that has an included angle of about 14 degrees. One tube has been trimmed to fit over the other and the fit between the two is pretty tight, no gaps larger than about 0.01 inches. I am welding with a Dynasty 200DX using 1/16 inch ER70-S2 and a current of 55 amps. The tubes are about 10 feet long and I want their ends to be separated by 30 inches when finished. The tubes are held in a jig when welding starts and I begin by placing small tack about 2 inches apart over the full length of both joints. The weld tacks do not cause any perceptible warps---the part still has the desired geometry after tacking.I then make a complete weld between tacks, alternating sides and tack pairs. My problem is that when I am finished I find that shrinkage of the 10 inch-long weld has caused the included angle to be reduced with the result that the far ends of the tubes are separated by only 28 inches, not the 30 inches that I need. I attempted to post pictures of the part but was not successful in attaching them. If requested I will try again.Does anyone have recommendations for steps that will reduce the trouble I am having?JerrySan Antonio
Reply:Well, now that we know which direction it's warping, what about bending it the other way before welding, by a proportionate amount?Currently working as a Paralegal, but still interested in hobby welding.Miller Bobcat 225ntOne- Character Fractions: ¼ ½ ¾ ⅛ ⅜ ⅝ ⅞
Reply:Most of the time, it is best to begin with the end in mind.  Start with a gap of 32 inches and let it shrink to the desired 30 inches.  Smaller weld segments may help, but thin wall tubes are gonna shrink and move on you.Multimatic 200Ellis 1800Haberle S225 9" cold sawMM 300;  Spoolmate 30A w/ WC-24TB 302GDynasty 280 DX Tigrunner
Reply:Jerry welcome to the forum.Lincoln A/C 225Everlast P/A 200
Reply:Changing direction of your welds can impact the outcome as well.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:I would also try to use 0.035-0.045" wire instead of 1/16.  You're dumping in more heat than necessary to melt the 0.063" filler rod than you would with a 0.035-0.045" filler.  As we all know, excess heat contributes to shrinkage.  Generally speaking, the filler rod should not be thicker than the base metals you are trying to fuse, so you're only making it harder on yourself.  I'm not saying it will solve all your problems, but it will certainly help.Last edited by Oscar; 07-14-2015 at 01:37 PM. 1st on WeldingWeb to have a scrolling sig! HTP Invertig 400HTP Invertig 221HTP ProPulse 300HTP ProPulse 200 x2HTP ProPulse 220MTSHTP Inverarc 200TLP HTP Microcut 875SC
Reply:The above suggestions are right on point.  The only other suggestion I would make would be to tack a temporary brace between the V legs about 8" from where they meet to prevent the pull-in.Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:You're talking about a very small amount of warpage.  I would just grab the ends and pull them back apart.  Or are these space shuttle parts?My name's not Jim....
Reply:Have you seen this video?  http://www.weldingtipsandtricks.com/...istortion.html  Its worth a look-see.  There are some surprises there, based on the direction of bead travel.  Perhaps it would be worth picking up a cheap laser and perform the same test, attempt to develop a procedure (and repeatable direction of travel) that reduces the undesired shrinkage.  --Zip